1. Field
The present invention relates to wireless communication and, more particularly, to an apparatus and method for uplink synchronization in a multiple component carrier system.
2. Discussion of the Background
In a common wireless communication system, although an uplink bandwidth and is a downlink bandwidth are differently set, only one carrier is chiefly taken into consideration. In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), the number of carriers forming uplink and downlink is one based on a single carrier and the bandwidth of uplink and the bandwidth of downlink are symmetrical to each other. In this single carrier system, random access is performed using one carrier. As multiple component carrier systems are recently introduced, random access has been able to be implemented through several component carriers.
A multiple component carrier system means a wireless communication system capable of a carrier aggregation. The carrier aggregation is technology in which small fragmented bands are efficiently used, and the carrier aggregation creates an effect that uses a logically wide band by aggregating a plurality of physically continuous or discontiguous bands in a frequency domain.
A terminal performs a random access procedure in order to access a network. The random access procedure can be divided into a contention-based random access procedure and a non-contention-based random access procedure. The greatest difference between the contention-based random access procedure and the non-contention-based random access procedure lies in whether a random access preamble is dedicated to one terminal or not. An object of a terminal to perform a random access procedure on a network can include initial access, a handover, a scheduling request, and timing alignment.
In a multiple component carrier, in order to effectively perform timing alignment, a concept of a Timing Advance Group (TAG) is used. The TAG is a group of one or more serving cells having the same timing advance value and is configured in response to higher layer signaling. A base station can indicate that a secondary serving cell is included in what TAG for each secondary serving cell. For example, a base station can inform a terminal that a first secondary serving cell is included in a first TAG, a second secondary serving cell is included in a second TAG, and a third secondary serving cell is included in a first TAG, regarding the three secondary serving cells configured in the terminal.
However, a signaling protocol for informing that a secondary serving cell is included in what TAG has not yet been clearly defined. Furthermore, when a TAG to which a secondary serving cell belongs is changed according to a channel condition, whether a terminal will be informed using what method and how the method will be implemented have not yet been disclosed.